Hi guys,
I was working with PVC pipes for making a mock chassis recently, and i wanted to make it pretty close to the actual cad model. I tried a few things to attach the pipes rigidly to each other at joints using :-
1. PVC solvent (used to make joints leakproof in plumbing) - not strong enough
2. Duct tape - holds, but is not exactly as rigid as i'd like
3. Plaster of paris - Did not adhere to the PVC surface well, and was really brittle
I also tried melting the pipes into each other :P , but it was a bit of a disaster.

I could not use any fittings due to the oblique angles at joints.
Has anybody else faced this issue?
Can anyone point me in the right way?

Are you notching the pipes together as you would for welding? That alone will help with strength a lot, not to mention be good practice for the real thing.

I'd try hot glue for sticking the tubes together. Hot glue will cure pretty quickly, you can easily lay it on thick if you don't have a perfect fitment of tubes, and is mostly removable if you have to change something.

Mocking with PVC is not incredibly accurate, and should only be used as a very quick guide. In that case the tape is good enough.

I prefer to mock with steel. It is amazing how quickly you can mock something up with whatever cheap steel you can find. Just rough end preps and tacks and a group of 3 people could put together a full frame mockup easily in a day, that will be much more accurate and rigid than PVC.

In 2011 the mock (made in 2 half days) at ECU ended up as a rolling chassis with a lot if final parts attached. It was incredibly easy to do and informed the final chassis design much more than a month of solid modelling.